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Sage Thrasher Oreoscoptes Montanus

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Sage Thrasher Oreoscoptes Montanus Wyoming Species Account Sage Thrasher Oreoscoptes montanus REGULATORY STATUS USFWS: Migratory Bird USFS R2: No special status USFS R4: No special status Wyoming BLM: Sensitive State of Wyoming: Protected Bird CONSERVATION RANKS USFWS: Bird of Conservation Concern WGFD: NSS4 (Bc), Tier II WYNDD: G4, S5 Wyoming Contribution: LOW IUCN: Least Concern PIF Continental Concern Score: 11 STATUS AND RANK COMMENTS Sage Thrasher (Oreoscoptes montanus) has no additional regulatory status or conservation rank considerations beyond those listed above. NATURAL HISTORY Taxonomy: There are currently no recognized subspecies of Sage Thrasher 1, 2. On average, northern populations have longer tails than southern populations, indicating slight phenotypic differences between populations 1. Beyond this, there is no evidence supporting subspecific designation. Description: Identification of Sage Thrasher is possible in the field. Sage Thrasher is a medium sized passerine and is the smallest thrasher species 1. Males are slightly larger than females, but plumage is similar for both sexes 1. Adults are generally drab brown-grey. The head is characterized by an indistinct whitish supercilium, whitish leading edge of the nape, and whitish malar with thin black submoustachial stripe. Underside is lighter and breast, sides, flanks, and belly have distinct dark streaking. Back and wings are brown-grey. Wings have two narrow, crisp wing-bars 1, 3, 4. Juveniles are similar in appearance, paler overall with less distinct streaking on underside 1, 3, 4. The species is distinguished from other thrashers by its smaller size and short, straight bill 1. Sage Thrasher is similar in appearance to Bendire’s Thrasher (Toxostoma longirostre). Bendire’s Thrasher has small triangular spots on its breast while Sage Thrasher has streaks on its breast and crisp white wing-bars 4. Distribution & Range: Sage Thrasher breeds from northern New Mexico and Arizona north to extreme southern British Columbia. Wyoming constitutes a relatively large portion of the breeding range and marks the northeastern edge of summer range. Confirmed or suspected breeding has been documented in Page 1 of 7 Wyoming Species Account all of the state’s 28 latitude/longitude degree blocks 5. Sage Thrasher migrates south and winters in the southwestern United States, central Mexico, and Baja Peninsula. There are no known range contractions or expansions. But local extinctions have been observed in some areas that have undergone significant habitat alteration 1. Habitat: Sage Thrasher is considered a sagebrush obligate species 1, 3. In Wyoming and other parts of its range, the species is found in shrubsteppe habitats dominated by big sagebrush (Artemisia spp.). The species is occasionally found nesting in desert shrublands with Black Greasewood (Sarcobatus vermiculatus), rabbitbrush (Chrysothamnus spp.), and Bitterbrush (Purshia tridentata) 3. In other portions of their range, they may be found in semi-arid grasslands and juniper woodlands 3. Sage Thrasher typically nests in large, healthy sagebrush shrubs. Shrubs greater than 70 cm in height and with greater than 75% living canopy are generally selected for nesting 3. Additionally, Sage Thrasher is typically associated with areas of higher than average cover and height of sagebrush shrubs 3. In Wyoming, Sage Thrasher is most common in areas with contiguous tracts of healthy sagebrush steppe. Specifically, Sage Thrasher is common in the Upper Green River Basin, Great Divide Basin, and Big Horn Basin. Habitat use during migration and non-breeding season is more general than during breeding 1, 3. Sage Thrasher is still typically found in shrubsteppe habitats including mixed desert shrublands, arid grasslands with shrub cover, and open pinyon-juniper woodlands 1, 3. Phenology: Sage Thrasher arrives in Wyoming in mid to late March and departs for wintering grounds in August through early October 1. In Wyoming, Sage Thrasher establishes territories and nest shortly after arriving in the breeding range 1. Inter-annual timing of seasonal migration and nesting is dependent upon weather conditions and may vary by several weeks. Diet: Sage Thrasher feeds primarily on insects, but berries and other small fruits are consumed when available 1, 3. CONSERVATION CONCERNS Abundance: Continental: WIDESPREAD Wyoming: COMMON In 2013, Partners in Flight estimated that Sage Thrasher had a global population of approximately 5.9 million individuals and a Wyoming population of approximately 1 million 6. The species has a statewide abundance rank of common and appears to be common within suitable environments in the occupied area 5. From 1968–2015, annual Wyoming Breeding Bird Survey (BBS) detections of Sage Thrasher ranged from 13 to 1,015 (average = 521), with 531 recorded in 2015 7. Annual detections of Sage Thrasher ranged from 264 to 559 during surveys for the Integrated Monitoring in Bird Conservation Regions (IMBCR) program between 2009– 2015 8. Estimated mean density across this same time period was 2.31 birds per km2 (standard deviation 0.63, standard error 0.24) in suitable habitats in Wyoming 8. Population Trends: Historic: MODERATE DECLINE Recent: STABLE Page 2 of 7 Wyoming Species Account Wyoming trend data from the North American BBS indicate that Sage Thrasher declined by 0.53% annually from 1968–2013 and 1.94% annually from 2003–2013; however, neither state estimate was statistically significant 9. Survey-wide BBS trend data indicate that Sage Thrasher numbers experienced a statistically significant annual decline of 1.39% from 1966–2013, and a non-significant annual decline of 1.21% from 2003–2013 9. Intrinsic Vulnerability: MODERATE VULNERABILITY Sage Thrasher has a high degree of habitat specificity, preferring contiguous stands of healthy, mature sagebrush 1, 3. For example, along a successional gradient of sagebrush steppe habitat, Sage Thrasher was strongly associated with mature sagebrush as opposed to recently burned sagebrush or juniper-sagebrush mosaic in Oregon 10. Similarly, in Wyoming, Sage Thrasher was negatively associated with areas that had undergone controlled burning 11. Furthermore, it appears that requirements for suitable nesting habitat are quite narrow, being restricted to large, healthy sagebrush shrubs 3. Extrinsic Stressors: MODERATELY STRESSED Research indicates that the largest threat to Sage Thrasher is habitat loss, degradation, and fragmentation 1, 3, 12. Evidence suggests that Sage Thrasher abundance was negatively correlated with grass cover in Washington State 1. Sagebrush steppe habitats in portions of Wyoming have experienced large-scale invasions of Cheat Grass (Bromus tectorum). It is likely that this negatively affects Sage Thrasher populations in the state. Additionally, cheat grass increases fire frequency in sagebrush ecosystems 12. It is well established that Sage Thrasher avoids burned areas 10, 11, 13. In Wyoming, sagebrush habitats have also been fragmented by energy development, including traditional oil and gas, coal bed methane, and wind power. Patterns of sensitivity to habitat fragmentation are mixed and may be context dependent. For example, reproductive success of Sage Thrasher was lower in habitats fragmented by agriculture 14 and energy development 15. However, abundance of Sage Thrasher was not influenced by the density of natural gas wells. Reproductive success of Sage Thrasher was lower in energy development areas 15. Increasing energy development in Wyoming may lead to population declines of Sage Thrasher. KEY ACTIVITIES IN WYOMING Sage Thrasher is classified as a Species of Greatest Conservation Need (SGCN) by the Wyoming Game and Fish Department (WGFD), and as a Level II Priority Bird Species requiring monitoring in the Wyoming Bird Conservation Plan 16. The WGFD, Bureau of Land Management (BLM), and United States Forest Service have implemented increased monitoring efforts for Sage Thrasher and other sagebrush songbirds 17. In 2004 and from 2008 to present, the WGFD has funded graduate research at the University of Wyoming, in conjunction with the Wyoming Cooperative Fish and Wildlife Research Unit, to examine potential effects of oil and natural gas development on Sage Thrasher and other sagebrush-obligate songbirds in Wyoming 15, 18-22. From 2011 to present, the WGFD has funded graduate research to determine if state-wide efforts to conserve the Greater Sage-Grouse (Centrocercus urophasianus) may simultaneously benefit other SGCN species, including Sage Thrasher 23. In 2016, the WGFD funded an additional project to examine the effects of climate on nongame sagebrush bird demography and populations. Field work is scheduled to begin in 2017. The BLM funded research from 2010– 2012 to examine the potential effects of natural gas extraction infrastructure (i.e., roadways and Page 3 of 7 Wyoming Species Account well pads) on the distribution of sagebrush-obligate songbirds, including Sage Thrasher, at a natural gas field in southern Wyoming 24. ECOLOGICAL INFORMATION NEEDS Data regarding both abundance and population trends are lacking for Sage Thrasher. Also, a better understanding of how habitat loss and fragmentation affects this species is needed. MANAGEMENT IN WYOMING This section authored solely by WGFD; Zachary J. Walker. Sage Thrasher is classified as a SGCN in Wyoming due to habitat degradation and fragmentation. Broad scale monitoring efforts, such as the BBS and IMBCR, should be continued. Additional research should focus on addressing ecological information needs, and should
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